Demands for higher data rates for mobile services are steadily increasing. At the same time, modern mobile communication systems as 3rd Generation systems (3G) and 4th Generation systems (4G) provide enhanced technologies, which enable higher spectral efficiencies and allow for higher data rates and cell capacities.
In the Universal Mobile Telecommunication System (UMTS) radio resource management of User Equipment (UE) is mainly carried out by means of the Radio Resource Control (RRC) protocol, as specified by the 3rd Generation Partnership Project (3GPP) specifications, e.g. in 3GPP Technical Specification (TS) 25.331 V10.4.0 (2011-06). A mobile transceiver or UE that has an RRC connection can transmit and receive user traffic in CELL_DCH and CELL_FACH states. CELL_FACH state is usually for low and bursty traffic activity whilst CELL_DCH state is for high and often continuous traffic activity. CELL_DCH determines the state in which the UE has an active data connection to the network.
In CELL_DCH the UE has an active set consisting of cells that the UE can simultaneously communicate with, while utilizing circuit switched or uplink packet switched connections, which can also be referred to as dedicated connection. In other words, the UE is assigned permanent radio resources, as e.g. time, frequency and/or code resources, to transmit and receive data to and from each of the cells in the active set. That is, the UE can perform Soft HandOver (SHO) with these cells. SHO allows these cells to control the UE uplink transmission thereby controlling their uplink interference. SHO can increase the performance of uplink and downlink transmissions since it can benefit from diversity gains, as e.g. selective and soft combining.
In CELL_FACH, UEs in an overlapping coverage of two cells cause interference to their neighboring cells. While multiple cells can receive the uplink transmissions from a UE when in CELL_DCH using Soft HandOver (SHO), SHO is not possible in CELL_FACH. Hence, there is nothing the neighbor cell can do to reduce its interference. In the past, CELL_FACH was designed for short bursts of transmission and it acts as a temporary state, and hence a UE in the overlapping coverage would not cause prolonged interference.